1. Field of the Invention
The present invention relates to a solenoid valve driving circuit for driving a solenoid valve by applying a first voltage with respect to a solenoid coil of the solenoid valve during a first period, and for maintaining a driven state of the solenoid valve by applying a second voltage with respect to the solenoid coil during a second period following the first period, as well as to a solenoid valve having such a solenoid valve driving circuit, and a solenoid valve driving method therefor.
2. Description of the Related Art
Heretofore, it has been widely practiced to arrange a solenoid valve midway along a fluid passage, and by applying a voltage to a solenoid coil of the solenoid valve from a solenoid valve driving circuit, to energize the solenoid valve in order to open and close the fluid passage. In this case, during a first period (activation time), the solenoid valve is activated by applying a first voltage to the solenoid coil from the solenoid valve driving circuit, and during a second period (maintenance time) following the first period, the solenoid valve is retained in a driven state by applying a second voltage to the solenoid coil from the solenoid valve driving circuit.
In recent years, in the aforementioned type of solenoid valve, it has been desired to drive the solenoid valve with low power consumption. In Japanese Patent No. 4359855, it has been proposed that by turning a switch ON and OFF based on current that flows through the solenoid coil, conduction (electrical continuity) between a power source and the solenoid coil is controlled, whereby the solenoid valve can be retained in a driven state using an even lower amount of power consumption.
On the other hand, there is a concern that when the solenoid valve is used over prolonged periods, the driving performance of the solenoid valve may become degraded. Consequently, in Japanese Patent No. 3530775, it has been proposed to detect operating times of the solenoid valve, and by judging whether or not switching operations of the solenoid valve are normal, to enable notification beforehand as to whether the solenoid valve is functioning abnormally before the solenoid valve suffers from a catastrophic fault.
Incidentally, during a first period when the solenoid valve is activated, a comparatively large amount of electrical energy (power) is supplied to the solenoid coil in order to quickly activate the solenoid valve, whereas during a second period when the solenoid valve is maintained in the driven state, a lower amount of electrical energy is supplied to the solenoid coil, whereby the solenoid valve that was activated during the first period is maintained in the driven state.
Concerning the second period, as noted above, by means of the technology of Japanese Patent No. 4359855, low power consumption can be obtained adequately.
However, in contrast thereto, concerning the first period when a comparatively large amount of electrical energy is supplied to the solenoid coil, from the standpoint of providing a solenoid valve having lower power consumption, it has been desired to be able to activate the solenoid valve using lower electrical energy, or more specifically, to activate the solenoid valve with a small activation current value, and with a short activation time.